Ayatollah Jannaati of Iran affirms the permissibility of a women serving as prayer leader for other women:

Fatwa, posted 4.22.2010, from Iran, in:
Religious Authority: 
Mohammad Ebrahim Jannati
Fatwa Question or Essay Title: 
Ayatollah Jannaati of Iran affirms the permissibility of a women serving as prayer leader for other women:

A woman may serve as prayer Imam (leader) for other women.

٧. آيا زن جايز است براى زنان امام جماعت شود؟ بله جايز است.